Wireless automatic meter reading (AMR) systems are well known. Typically, each utility meter is provided with a battery-powered encoder that collects meter readings and periodically transmits those readings over a wireless network to a central station. The power limitations imposed by the need for the encoder to be battery powered and by regulations governing radio transmissions effectively prevent direct radio transmissions to the central station. Instead, wireless AMR systems typically utilize a layered network of overlapping intermediate receiving stations that receive transmissions from a group of meter encoders and forward those messages on to the next higher layer in the network as described, for example, in U.S. Pat. No. 5,056,107. These types of layered wireless transmission networks allow for the use of lower power, unlicensed wireless transmitters in the thousands of endpoint encoder transmitters that must be deployed as part of a utility AMR system for a large metropolitan area.
Synchronization between a transmitter and a receiver in an AMR system can be accomplished by using an encoded preamble at the beginning of each transmission. A correlator is then used to synchronize an incoming sampled data stream with a known sync pattern once a phasing arrangement partitions the sampled data stream into a first and second sampled sequences. In a wireless meter reading system, for example, where cost and battery power are central concerns, undesirable consequences of stabilization circuitry can erect a significant manufacturing and system design barrier.
One challenge faced by designers of wireless meter reading systems involves providing adequate coverage with transceivers located in the field that are receiving data from metering units that will be transmitted back to the utility. Current meter reading systems use high sensitivity receivers placed on utility poles to read as many meter modules as possible. These receivers are expensive and therefore must cover a large area. Signal multipathing and attenuation due to buildings, fences, and other structures cause holes in the coverage area. In order to fill these holes, additional receivers have to be placed in the coverage area, increasing the cost of the system. Additional transceivers may also be needed to provide reliable communications with meter modules located near the periphery of the coverage area and in only marginal communications range of a presently installed system transceiver. As housing development expands the areas needing communications coverage, utilities can experience the problem of overcapacity—that is, investing in expensive transceivers having high-sensitivity, high-capacity receivers for servicing new developments having far fewer meter modules than such receivers can accommodate. A goal in designing these systems is to achieve a balance of coverage and hardware invested in the meter reading system.
Installation of additional transceivers presents further challenges for utility providers. Typically, system transceivers utilizing high-sensitivity, high-capacity receivers include circuitry that operates continuously, or with high enough duty cycles, and consuming enough power, to require externally supplied electrical energy. In practice, locations determined to be desirable for system transceiver placement often do not have easily accessible line power. Tapping power distribution circuits and running wires dedicated to powering additional system transceivers presents substantial burden and cost for utilities.
Another challenge faced by utilities is the implementation and management of energy-saving load shedding programs. The lack of access to real-time data on the amount of actual energy still being used once load-shedding commands are sent to an electrical load is a typical problem encountered in load shedding program execution. Utilities have no way of knowing if a load shedding command, sent to a designated home or industrial location, has been overridden by the customer. In this example, the utility has no real-time data as to how much energy is actually being preserved in spite of the implementation of load shedding programs.